Thursday, November 10, 2011

SVP Part 1: Enormous, amazing, soaring birds

Posted by
Michael Habib

Over the next week I will be posting a bit about some of the talks and poster sessions I attended at SVP. I am going to begin, however, with a bit about the presentation that Justin and I presented (because heck, it is our blog, after all).

Our talk was entitled "Flight Performance of Giant Pseudodontorn Birds". As the title suggests, we were working with material from some of the largest flying birds in history. Our results, in fact, may help explain how they obtained such sizes in the first place.

What are pseudodontorns?

Pseudodontorns were extraordinarily long-winged seabirds with a duration of nearly 55 million years in the fossil record (Paleocene/Eocene to Pliocene) - the wonderful image above is by Greg Paul (he owns the image; don't use without permission). Some of the California specimens preserve feather impressions which allow us to make a quite good estimate of wing shape. Typically, the long, narrow wings of pseudodontorns have been interpreted as adaptations to a soaring regime similar to albatrosses. However, albatrosses have a rather specific specific soaring mechanism that is enabled by their high wing loading. An alternative, looking at modern birds, would be a frigate bird type flight strategy, but the overall morphology of giant pseudodontorns (span, size, etc) seems at odds with this particular strategy (frigates are highly maneuverable kleptoparasites - they steal fish from other birds). See the wonderful photo below of a frigatebird, taken by Chris Hobaugh (note the extremely broad wings).

Our answer is a third strategy: Justin and I suggest that giant pseudodontorns, such as Pelagornis, were "globe trotters" - that is, our analysis indicates that they were adapted to extreme flight range. This update comes, in part, from using new mass estimates from an exceptionally complete specimen found in Chile. It turns out that pseudodontorns had such elongate wings that mass estimates extrapolated from other seabirds produce overestimated body masses. The new, lower, body masses suggest that Pelagornis and kin combined a very high aspect ratio wing shape with rather low wing loading. This would enable highly efficient flight (glide ratio of 27:1 - the highest for any bird) and the ability to use micro-lift sources. Such an animal would not be able to soar fast like an albatross or turn on a dime like a frigate, but the potential time in the air and maximum range could have been quite extraordinary.

The new mass estimates also modify our thoughts on the limb strengths of pseudodontorns. It turns out that they had rather strong hindlimbs compared to, for example, a living albatross. Because launch is hindlimb driven in birds, this might mean that pseudodontorns had more juice over short takeoff sprints, and therefore a larger maximum size for effective takeoff.

This would enable highly efficient flight (glide ratio of 27:1 - the highest for any bird) and the ability to use micro-lift sources. Such an animal would not be able to soar fast like an albatross or turn on a dime like a frigate, but the potential time in the air and maximum range could have been quite extraordinary.

About this Blog

This blog is dedicated to discussions and news related to vertebrate paleontology, particularly animals from the Mesozoic (dinosaurs, pterosaurs, and others). This blog is the work of two paleontologists from U.S. West Coast: it is the work of Justin Hall and Michael Habib, both at the University of Southern California in Los Angeles.

All opinions on this site reflect the views of their author only and do not reflect the viewpoint of the universities and museums the author may work for, or with.